a few prelim IM programs specifically request a chair or departmental letter by the chair of the IM department or a designee, typically the IM clerkship director. it's a requirement of all the categorical IM applicants, but some (like stanford) want to see it for the prelims, too. at most schools it is a form letter written by the IM clerkship director who usually doesn't know you from Adam, summarizing your performance on the rotations, with comments that already appear in the MSPE. so, in my opinion, it's totally useless. TYs don't want or need one. I'm sending the same four to TYs and Rads. the key is to have a couple strong clinical letters, preferably one from medicine, with someone who really knows you and can speak to your strengths.